The present invention relates to optical storage devices and more paticularly to improved techniques for optical imaging with surface wave convolvers.
Various techniques for information storage have recently been advanced which rely on the storage of signals in depletion layers in the surface of semiconductor substrates. These techniques use structures known as charge coupled devices and have allowed many improvements in information storage and transfer. The conventional charge coupled device is constructed by mounting a metal electrode on the surface of a semiconductor with an oxide or insulator sandwiched therebetween. The application of a bias voltage across the substrate and electrode then causes a depletion layer under the electrode whose thickness, and therefore information content, is determined by the value of voltage applied. While such devices have wide applications, special structures and electrode configurations are required, thereby rendering the devices relatively complex.
Still other devices have been proposed wherein a piezoelectric semiconductor substrate is used as the storage medium for an optical image. In such devices an electrode is mounted on a piezoelectric substrate separated therefrom by an epitaxial layer. A biased voltage applied to the electrode causes charging of the substrate surface to a predetermined level beneath the Schottky barrier electrode. When an optical image is projected through the electrode, areas of the surface illuminated by the light are discharged in proportion to the light intensity while the remaining surface areas retain a charge pattern which can be read by utilizing standard acoustic surface wave techniques. While optical imaging is attained, the device requires a piezoelectric semiconductor substrate to provide optical readout, which material is not as widely available as a more common semiconductor. In addition, the device provides storage times which are relatively short, on the order of minutes, with special temperature conditions and segmented electrodes necessary for optical imaging.
While still other techniques are known which allow optical imaging and storage, each suffers from limitations on storage time and structure complexity, and none have allowed long storage times at room temperatures with nondestructive acoustic surface wave readout.
Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to provide a relatively simple and inexpensive system for storing optical information.